There was no heaven or earth, and there was no land. Only three gods who were combined as one and began to reproduce, creating many of the gods.
Ea - Generations
Eventually, Ea was born and became one of the most clever gods. Eventually, his descendants and more of the gods were becoming an unruly crowd.
Plans of Murder
Apsu approached his wife Tiamat and told her that he planned to murder their unruly descendants and she would not stick to her husband's gruesome plans. He decided to carry on with his plan anyway.
Ea heard of Apsu's scheme and decided to strike. He cast a spell on Apsu and took his crown, slaying Apsu in the process and building a castle upon his waters. There he fathered the creature Marduk.
Tiamat was furious with Ea and approached him with an army of dragons and monsters and commanded Kingu as her general. Ea was worried that it would be a losing battle, so he asked Marduk to fight in his place. Marduk gladly accepted and slew Tiamat, shooting an arrow down her throat, piercing her heart.
The True Creation
Marduk took a club and split Tiamat's body in half to create the heavens and the earth. He made rivers flow from her eyes. After he had finished, he created all the plants and animals. Eventually, the gods who had sided with Tiamat were put into labor and began to rebel. To make up for this, Kingu was slain and humans were created with his blood, which he assigned to labor.